1. Field of the Invention
The present invention relates generally to connecting electronic devices in dc series, and in either rf series or parallel. More particularly, the present invention pertains to connecting electronic devices in dc series, precisely proportioning a dc source voltage to selected ones of the electronic devices irrespective of production variations in component operating parameters or drift in component parameters, and rf decoupling the dc series-connected electronic devices.
2. Description of the Related Art
Frequently, maximum operating voltages of solid-state electronic devices are too low for the dc source voltage that is available. By connecting the solid-state electronic devices in dc series, the dc source voltage may be divided between, or among, a plurality of solid-state electronic devices, either equally or proportionally, as desired, thereby providing dc voltages that are usable for any desired type of solid-state electronic device, and thereby also sharing the same dc current flow.
Since the solid-state electronic devices are stacked in series between a dc source voltage and an electrical ground, this type of electronic system has been called a “totem-pole” electronic circuit. However, since all of the solid-state electronic devices share the dc current, herein this type of electronic system is called a “shared-current electronic system.”
The dc source voltage may be divided either proportionally or variably, and other types of electronic devices, such as bandwidth processors, may be connected in dc series with an other solid-state electronic device. The inputs and outputs of the electronic devices, whether rf or lower frequencies, may be connected in either series or parallel.
As an example of equal or proportional division of the dc source voltage, gallium arsenide field-effect transistors (GaAsFETs) are the primary solid-state devices used for amplification of high frequency signals in the range of 3.0 GHz and higher. GaAsFETs have the advantages of being readily available and relatively inexpensive. However, a major disadvantage of GaAsFETs is that the maximum operating voltage is commonly +10.0 volts dc.
For many transmitter/amplifier applications, particularly airborne applications, the dc source voltage is 28.0 volts dc, plus or minus 4.0 volts dc. Since gallium arsenide FETs have an operative voltage of +10.0 volts dc, the use of gallium arsenide FETs has presented a problem.
Traditionally, there have been two solutions to this problem: linear voltage regulators and switching voltage regulators. Linear voltage regulators have the disadvantages of excessive heat generation and low power efficiency. And, switching voltage regulators have the disadvantages of increased cost, space inefficiency, and the creation of a spurious signal on the rf carrier (EMI problems) due to the switching action of the regulator.
A third approach to solving the problem of disparity between the operating voltage of solid-state devices and a dc source voltage has been to connect the solid-state electronic devices in dc series, thereby dividingly sharing the dc source voltage and utilizing the same current flow. This shared-current approach was presented in IEEE Transactions on Microwave Theory and Techniques, Volume 46, Number 12, of December 1998, in an article entitled “A 44-GHz High IP3 InP-HBT Amplifier with Practical Current Reuse Biasing.”
Shared-current electronic systems solve the problem of the disparity between the operating voltage of solid-state devices and a higher source voltage. Two or more solid-state electronic devices are connected in series for dc operation.
That is, current that flows in series through the solid-state devices is used two, or more, times in the production of the rf output. The dc current is used once in each of two, or more, series-connected solid-state electronic devices, thereby increasing the rf output for a given current flow, as compared to rf amplifiers connected in the conventional fashion.
However, shared-current electronic systems have been used only at low rf powers, as in the above-referenced article wherein the power was in the order of 100.0 milliwatts. At higher rf powers, problems associated with inadequate rf decoupling have included low power efficiency, oscillation, a decrease in reliability of the circuits, and destruction of the solid-state devices.
Power limitations with regard to aforesaid problems were solved by Lautzenhiser et al., as taught in U.S. Pat. No. 6,683,499 that issued on Jan. 27, 2004, and which is incorporated herein by reference thereto.
Although there was nothing in the literature that hinted of rf power limitations for shared-current systems, factors that might cause component failure at higher rf powers, or solutions to any such problems, Lautzenhiser et al. solved this rf power limitation of shared-current electronic systems by providing improved rf decoupling.
More particularly, Lautzenhiser et al. teach providing rf decoupling with an effective series resistance that is less than that of the best capacitors, namely porcelain capacitors. Providing rf decoupling with an effective series resistance that is lower than that of the best capacitors is achieved by paralleling porcelain capacitors. Capacitors are parallel to provide these reduced effective series resistances at single frequencies or over a band of frequencies by paralleling a plurality of capacitors that resonate at the same or spaced-apart frequencies.
While one reason for connecting solid-state devices includes the low operating voltages of GaAsFETs with respect to the dc source voltage, an other reason for connecting solid-state devices in series is to variably proportion the dc source voltage between, or among, two or more solid-state electronic devices.
The dc source voltage may be variably proportioned between, or among, two or more solid-state electronic devices for the purpose of phase shifting an rf output as taught by Lautzenhiser et al. in U.S. Pat. No. 6,690,238 which issued on Feb. 10, 2004, and which is incorporated herein by reference thereto.
The dc source voltage may also be variably proportioned for the purpose of variably shifting or proportioning, or even rapidly switching, rf power from one antenna to an other, as taught by Lautzenhiser et al. in U.S. Pat. No. 6,747,517 which issued on Jun. 8, 2004, and which is incorporated herein by reference thereto.
Further, as taught by Lautzenhiser et al., in U.S. patent application Ser. No. 10/644,115, filed Aug. 20, 2003, a solid-state electronic device, such as a FET, may be connected in dc series with a processing electronic device, such as an oscillator or a baseband processor, that may include hundreds of discrete components. By dc series-connecting the solid-state electronic device and the processing electronic device in dc series, and proportionally dividing the dc source voltage between the devices, a dc voltage suitable for each device is provided, the dc current is shared, the use of a voltage regulator is obviated, and power efficiency is increased greatly.
As taught in the above-referenced U.S. patent application, an important use of shared-current electronic systems is in spectrally-efficient digital modulation systems such as SOQPSK (Tier I) or multi-h CPM (Tier II) in which the quantity of data in a given bandwidth is doubled or tripled respectively as compared to the PCM/FM (Tier 0) waveform. Importantly, the shared-current principle also increases the power efficiency of electronic systems that use Tier 0, Tier I, and Tier II waveforms, since all three waveforms (Tier 0, Tier I, and Tier II) may be produced by the same hardware by making a change in the software.
Unless rf decoupling is provided as taught by Lautzenhiser et al. in U.S. Pat. No. 6,683,499, reduced efficiency will certainly occur, and both instability and destruction of the solid-state electronic devices may occur. More particularly, if one of the solid-state electronic devices goes into unstable self-oscillation, it will consume more dc bias and most likely become over biased resulting in destruction of the solid-state device.
In a shared-current configuration that uses FETs, all FETs may be destroyed if one FET fails, depending on how the first FET fails. For example, if the upper FET oscillates and consumes the dc bias, it will be over-biased and will be destroyed. If, in the destruction, the drain and source short circuit, which is a common type of failure, the lower FET will be over-biased, too, so that the lower FET will also fail.
Inadequate rf decoupling, at the very least results in poor efficiency. At the worst, and with higher likelihood at higher rf outputs, it results in destruction of the FETs and/or damage or destruction of circuits connected to the FET inputs and outputs.
However, even though adequate rf decoupling, as taught by Lautzenhiser et al., allows higher, and seemingly almost unlimited rf outputs, production variations of component operating parameters and drift of component operating parameters caused by aging and temperature variations combine to provide an other limitation to rf power outputs.
More particularly, when solid-state electronic components are connected in dc series between a dc source voltage and an electrical ground, an increase, or a decrease, in the percentage of the dc source voltage that is used by one of the solid-state electronic components inversely affects the percentage of the dc source voltage that is applied to the other solid-state component(s). This problem is compounded if more than two solid-state electronic components are connected in dc series.
Therefore, production variations in component parameters, with or without drift of component parameters, can cause failure of one solid-state electronic component, and failure of one electronic component can cascade into failure of other solid-state electronic components, and also cause failure of input and output devices, in like manner as described above for failures caused by inadequate rf decoupling.
The present invention overcomes this additional rf output limitation by precisely proportioning percentages of the dc source voltage that are utilized by individual ones of the several dc series-connected solid-state electronic devices irrespective of production variation of component operating parameters and drift of component operating parameters. More particularly, an electronic device that is called a “precise proportioner” is connected to lower-voltage and input terminals of all of the dc series-connected solid-state electronic devices except for the one nearest the electrical ground.